The invention generally relates to a method for determining rates of heat transfer, and more particularly relates to a method for determining differences or changes in the rate of heat transfer through tube walls.
In nuclear reactor steam generators, a gradual decrease in outlet pressure has been noted. This pressure loss has been attributed in part to fouling on the secondary side of the steam generator heat-transfer tubes. In order to determine whether it would be economically advantageous to remove these deposits from the tube walls, particularly from the outer walls of the tubes, an accurate method is needed to determine the change in the rate of heat transfer through a tube wall before and after it has been cleaned.
It is well known that the rate of heat transfer through the wall of a tube can be determined by pumping hot water through the tube and measuring the quantity of heat that is transferred to a fluid outside the tube. However, this technique requires an expensive calorimeter, and can be both difficult and costly when the tube is radioactively contaminated, as the water that is pumped through the tube is likely to become radioactively contaminated.
Other direct techniques that are known for measuring changes in heat transfer rates do not take into account the specific geometry of a steam generator tube. Removal of deposits from the surface of a tube will reduce the heat transfer area of the tube. For example, the removal of a 10 mil thick deposit from the outer surface of a 0.5 inch OD tube will reduce the outer surface area of the tube by 4%. Therefore, in order to determine the difference in the rate of heat transfer through a tube wall before and after cleaning, it is necessary to consider both the change in the heat transfer coefficient of the tube wall due to the removal of deposits, and any changes in the total heat transfer area of the surface of the tube that would result from the cleaning process.